TODAY | October 17, 2012
>>> world class art has police following up in london. next's keir simmons has more.
>> reporter: the 15 tips from the public came after an alert went out around the art world , but people are asking how some of the world's most valuable pictures could be stolen with such apparent ease. part of the art world 's heritage, among them pieces by picasso , monet, gaugin, freud, works that could be worth around $100 million and irreplaceable. stolen from this museum in rotterdam where only matisse 's reading girl in white and yellow had been displayed. there is now an empty space . europe's art experts are stunned.
>> it's a very significant loss, both to the public and to the trust which owns the pictures. it's very sad. we hope to get them back. it may take us many years
>> reporter: pictures lifted from the walls like a clock from the movie "the thomas crown affair ." by the time the alarm sounded and police arrived, the thieves had left.
>> very modern security system in this museum, and the alarm response was very quick, so thieves were not able to steal many paintings.
>> reporter: europe has seen a series of art heists. two years ago a pallies gallery was raided. pictures by matisse and picasso are still missing from that theft. in 2004 , "the scream" by edwa monk was taken and even "the mona lisa " was stolen from the louvre.
>> it's very impressive when you can open up your den and see a great piece of artwork, whether it's a matisse or a picasso .
>> reporter: the artworks taken this week like the pablo picasso piece is so well known they cannot be sold on the open market , but some expert fear they may end up as collateral for a bad debt in the underworld. now perhaps there was inside information because there were no guards on duty overnight when the raid happened at the museum. instead, they relied on cameras and alarms which seems incredible, natalie, because getting the pictures back will be a tough job. around 20% of artwork stolen like this are never recovered.
>> amazing. keir simmons , thanks so much.